Recovering a number from its sum and product

Recovering a number from its sum and product

Junior College 1
6 marks

A complex number \(z\) satisfies \(z+z^*=6\), \(zz^*=25\) and \(\operatorname{Im}(z)>0\).

  1. Find \(z\).[3]
  2. Find \(z-z^*\).[1]
  3. Use the given sum and product to find \(\dfrac1z+\dfrac1{z^*}\), without evaluating the two reciprocals separately.[2]

Solution:

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Answer:(a) \(z=3+4i\) (b) \(8i\) (c) \(\dfrac6{25}\)

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